Automated data storage libraries are known for providing cost effective access to large quantities of stored data. Generally, automated data storage libraries include a large number of storage bins in each of which is stored a portable data recording medium. The typical portable data recording medium is a tape cartridge or an optical cartridge. An accessor or accessors typically accesses the data recording media from the storage bins and delivers the accessed media to a read/write recording device for reading and/or writing data on the accessed media. Suitable electronics, such as a library controller, both operates the accessors and transmits and/or receives data between an attached on-line host computer system and the read/write recording devices. A component of each library controller is often one or more data storage drives which contain the program for operating the library and tables for tracking the data stored in the portable data recording media and the bins in which the media are stored.
In a conventional automated data storage library, the storage bins are arranged in a planar orthogonal arrangement forming a "wall" of storage bins for holding data recording media. The plane may be a flat plane, or may be a cylindrical plane. To double the storage capacity, two "walls" of storage bins may be provided on either side of the accessors.
A number of different companies manufacture automated data storage libraries today, each model displaying various different features. Some of the automated data storage libraries have dual or multiple accessors to provide a level of redundancy, and some have dual library controllers to control the accessors, also providing a level of redundancy. One example is the dual accessor model IBM 3494 Data Storage Library. The redundancy may be for enhancing the access speeds, or to provide continuous operation in the event of a failure, or both. In some instances, complex electronic connections are made between the various accessors and various library controllers so that an electronic change can be made to alter the connections between the accessors and library controllers, for example, in the event an accessor fails or in the event a library controller fails.
As described above, automated data storage libraries provide a cost effective means of storing data. Such libraries typically come in a wide range of total cost, the higher cost systems typically providing the higher degree of redundancy. It would be advantageous in the lower cost environment to be able to provide a high degree of redundancy without the complex electronic connections.
Automated data storage library read/write recording devices may also fail and have to be replaced manually by service personnel and, if not replaced immediately, the library will run degraded until replaced.
Some automated data storage libraries have large cache memories for temporarily storing the data to be written or that has been read from the data recording media. One type of cache memory in use today is a plurality of data storage drives, such as magnetic disk drives, arranged in a RAID configuration. A RAID is a "redundant array of inexpensive disk drives" and stores data and parity amongst the disk drives in such a manner that, should one disk drive fail, the remainder may continue to operate without loss of any of the data. One example is the IBM 3494model B16 Virtual Tape Server. The RAID configuration does operate at a significantly slower speed with one failed disk drive. Thus, it would be helpful to be able to replace the failed drive as soon as possible. The replacement of the failed drive is typically done manually, in that service personnel will bring a similar disk drive to the RAID array and manually disconnect the failed drive and insert the similar disk drive. A high cost replacement procedure is to provide a "hot spare" drive, which is without data and which has complex electronic connections that allow the hot spare drive to be switched electronically into the RAID so as to assume the responsibility of the failed drive and improve performance immediately.